The present invention relates to microfabricated actuators, particularly to microactuators for use in catheter-based interventional therapies or remote micro-assembly applications, and more particularly to microfabricated therapeutic actuators utilizing shape memory polymer (SMP) microtubing as a release actuator mechanism, and to heating arrangements for SMP release mechanisms.
Microactuators for remote and precise manipulation of small objects is of great interest in a wide variety of applications. Recently, substantial efforts have been directed to the development of microactuators or microgrippers for various application, and which are particularly useful in the medical field, such as for catheter-based intervention therapies and remote assembly or use of micromechanical systems. There has been particular interest in the development of microactuators capable of operating in small (250-500 .mu.m) diameter applications, such as in veins and arteries in the human brain, which enables catheter-based devices to reach and treat an aneurysm in the brain.
A recent approach to satisfying this need involves microactuators or microgrippers fabricated using known silicon-based techniques or precision micromachining, or a combination of these techniques, with the microgrippers being actuated, for example, by balloons or by shape-memory alloy (SMA) films or wires deposited on or connected to the jaws of the microgrippers. Such an approach is described and claimed in U.S. Pat. No. 5,645,564 issued Jul. 8, 1997, entitled "Microfabricated Therapeutic Actuator Mechanism," assigned to the same assignee. Another recent approach involves a miniature plastic gripper constructed of either heat-shrinkable or heat-expandable plastic tubing having a cut in one end section to form gripping surfaces or jaws which are moved by inflation or deflation of an associated microballoon. Such an approach is described and claimed in U.S. Pat. No. 5,609,608 issued Mar. 11, 1997, entitled "Miniature Plastic Gripper And Fabrication Method," assigned to the same assignee. Also, microdevices for positioning, steering, and/or sensor applications have been developed which utilize blood flow for positioning and steering of catheter-based therapeutic applications. Such microrudders, microactuators or microcantilevers are described and claimed in copending U.S. application Ser. No. 08/533,426, filed Sep. 25, 1995, entitled "Micromachined Actuators/Sensors For Intratubular Positioning/Steering," now U.S. Pat. No. 5,771,902 issued Jun. 30, 1998, assigned to the same assignee. In addition, recent efforts have been directed to the fabrication of micromolds for the production of microballoons used, for example, for angioplasty to perform interventional catheter-based minimal-invasive surgeries, wherein microballoons or microneedles having, for example, a 275 .mu.m length and 150 .mu.m diameter can be readily manufactured. Such a micromold is described and claimed in U.S. Pat. No. 5,658,515, issued Aug. 19, 1997, entitled "Polymer Micromold And Fabrication Process".
Patients with potentially life-threatening hemmorhagic brain aneurysms are in need of a safe, reliable, and fast release mechanism for the deposition of embolic platinum coils via catheters. The commercial product of current use is the Guglielmi Detachable Coil (GDC). The GDC utilizes the electrolytical dissolution of a designated guidewire junction to generate the release action. This procedure typically takes 10-30 minutes and is difficult to control in a reliable fashion. The effects of the dissolved material into the blood stream is also a potential hazard to the patient. Thus, even with the numerous prior efforts to develop miniature actuators for catheter-based therapeutic application, there remains a need for safe, fast release actuator mechanisms for the delivery of embolic coils, for example.
More recently, efforts have been directed to satisfy this need based on the use of a shape memory polymer (SMP), a polyurethane-based material that undergoes a phase transformation at a manufactured temperature (Tg) of choice. After the material is polymerized (cross-linked), the material is molded into its memory shape. At temperatures above Tg, the material can be easily reshaped into another configuration, and upon cooling below Tg the new shape is fixed, but upon increasing the temperature to above Tg, the material will return to its original memory shape. By inserting one end of a coil, for example, into an end of a SMP microtube, and applying pressures to the outside of the microtube while at a temperature above the Tg and then lowering the temperature below the Tg, the coil is secured and retained in the microtube. After inserting the microtube and retained coil via a catheter to a desired location, the SMP microtube is locally heated to above Tg and it returns to its original shape releasing the coil, after which the microtube is withdrawn leaving the coil in place. Therapeutic actuators utilizing shape memory polymer (SMP) microtubing are described and claimed in above-referenced U.S. application Ser. No. 08/807,412, now U.S. Pat. No. 5,911,737.
The present invention relates to therapeutic actuators utilizing SMP retention/release mechanisms and to heating options for SMP release mechanisms. In addition to embodiments involving the insertion of an end of a deposit material into the SMP tubing for retention thereby, the SMP tubing is inserted into an end of a deposit material which is retained thereby by expansion of the inserted SMP tubing (an inverted grip mechanism). The SMP heating options include resistive heating, optical laser light heating, and external field (RF, magnetic induction) heating. Also by coating the exterior of the SMP tubing with a reflective material enhanced light absorption in the SMP tubing is provided.